The remaining construction materials are deducted from the builder's
inventory as work on the ship progresses. A second fifth of the lumber
is required when the ship becomes 20% complete, a third fifth when the
ship becomes 40% complete, etc. Construction halts if the builder runs
out of materials

For example, a noble who wanted to build a galley would need to know
Shipbuilding [9503], have at least three workers, and start with at
least 10 wood [77]. (40 more wood is required to bring the galley to
completion).

As soon as the required number of worker-days has been invested in
construction, the ship will be christened and declared seaworthy.

To resume construction of a partially completed ship, first enter the
ship, then issue the either build galley or build roundship.

Ships may only be built in locations with a passable route to an ocean.